Method of transmitting and receiving downlink data in wireless communication system

ABSTRACT

A method of transmitting data through a downlink common transport channel in a wireless communication system is disclosed. The method comprises receiving measurement information transmitted from a user equipment at an upper network node, forwarding control information of the common transport channel, which is acquired from the measurement information, from the upper network node to a base station, and transmitting downlink data from the base station to the user equipment through the common transport channel in accordance with the control information.

This application is a 35 U.S.C. §371 National Stage entry ofInternational Application No. PCT/KR2007/005497, filed on Nov. 1, 2007,and claims the benefit of Korean Application No. 10-2007-00110821, filedon Nov. 1, 2007; U.S. Provisional Application No. 60/863,957, filed Nov.1, 2006; and U.S. Provisional Application No. 60/864,132, filed Nov. 2,2006, all of which are hereby incorporated by reference in theirentireties.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method of transmitting and receiving downlinkdata to and from a user equipment through a downlink common transmissionchannel of a wireless communication system.

BACKGROUND ART

In a universal mobile telecommunication system (UMTS) which is anasynchronous mobile communication system, a transport channel provides apath for data transmission between a physical layer and a medium accesscontrol (MAC) layer. Unlike a logical channel, various kinds oftransport channels can be used in accordance with occurrencecharacteristics of data which are transmitted. The transport channel canbe divided into two types of a dedicated channel and a common channel.The dedicated channel means a channel used dedicatedly by a specificuser equipment. The common transport channel is a channel that can beused commonly by a plurality of user equipments, and its examplesinclude a random access channel (RACH), a forward access channel (FACH),a broadcast channel (BCH), a paging channel (PCH), a high speed downlinkshared channel (HS-DSCH), a common packet channel (CPCH), and an uplinkshared channel (USCH).

Among the aforementioned common transport channels, examples of channelsused for downlink data transmission include FACH and HS-DSCH. Generally,the FACH is a downlink common channel used when a small number of dataare transmitted to a user equipment. The HS-DSCH is a downlink commontransport channel used for high speed data transmission in a high speeddownlink packet access (HSDPA) system. On the HS-DSCH, a plurality ofuser equipments share radio resources by using a plurality of commonchannelization codes. Each of the user equipments can be allocated witha plurality of channelization codes within a single transmission timeinterval (TTS) in accordance with its capacity, and data for theplurality of user equipments can be transmitted by code multiplexingwithin a single HS-DSCH TTI.

The FACH can be mapped with a secondary common control physical channel(S-CCPCH) which is a physical channel, and then can downwardly transmitdata dedicated for user equipment or common data. The S-CCPCH includes atransport format combination indicator (TFCI) field, a data field, and apilot field. The TFCI field notifies a transport format of datatransmitted to the data field. At this time, a radio network controller(RNC) of a network is in charge of scheduling of the FACH, and Node Bserves to transmit FACH data in a wireless manner through the S-CCPCH inaccordance with scheduling of RNC.

DISCLOSURE OF THE INVENTION

In the related art as described above, downlink data transmissionthrough the FACH which is one of downlink common transport channels hasa problem in that it is scheduled by a controller of a wireless networkand is not adapted to fast change in a state of a wireless channel.Also, a problem occurs in that downlink data transmission is notsuitable for high speed transmission due to a limited data transmissionrate.

Accordingly, the present invention is directed to a method oftransmitting and receiving downlink data in a wireless communicationsystem, in which data transmission can be adapted to status change of awireless channel.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, amethod of transmitting data through a downlink common transport channelin a wireless communication system is disclosed. In one embodiment ofthe present invention, an upper network node receives measurementinformation transmitted from a user equipment The network node delivers,to a base station, control information associated with the commontransport channel, which is acquired from the measurement informationand the base station transmits downlink data from the base station tothe user equipment through the common transport channel in accordancewith the control information.

In a method of transmitting data through a downlink common transportchannel in a wireless communication system in accordance with anotheraspect of the present invention, an upper network node receivesmeasurement information transmitted from a user equipment The networknode delivers at least a part of the measurement information to a basestation, and the base station transmits downlink data to the userequipment through the common transport channel by using the measurementinformation received from the network node. When transmitting thedownlink data, the base station determines a transmission power of aphysical channel mapped to the common transport channel, by using themeasurement information received from the upper network node, andtransmits the downlink data to the user equipment through the physicalchannel at the determined transmission power.

In still another aspect of the present invention, a method oftransmitting data through a downlink common transport channel in awireless communication system comprises receiving measurementinformation transmitted from a user equipment in an upper network node,forwarding control information related to the common transport channel,which is acquired from the measurement information, from the uppernetwork node to a base station, and scheduling downlink datatransmission to the user equipment through the common transport channelin the base station by using the control information.

In further still another aspect of the present invention, a method ofreceiving data through a downlink common transport channel in a wirelesscommunication system comprises transmitting measurement information toan upper network node, and receiving downlink data from a base stationthrough a physical channel mapped with the downlink common transportchannel, wherein a transmission power of the physical channel isacquired from the measurement information by the upper network node anddetermined in accordance with transmission power control informationforwarded to the base station.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a network architecture of a UMTS(Universal Mobile Telecommunications System).

FIG. 2 is a diagram illustrating a radio protocol architecture which isused in UMTS.

FIG. 3 is a flow chart illustrating a procedure according to oneembodiment of the present invention.

FIG. 4 is a diagram illustrating a protocol architecture in case wheredownlink data are transmitted to a user equipment through a forwardaccess channel (FACH) in accordance with the embodiment of FIG. 3; and

FIG. 5 is a flow chart illustrating a procedure according to anotherembodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, structures, operations, and other features of the presentinvention will be understood readily by the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Embodiments described hereinafter are examples in whichtechnical features of the present invention are applied to a UniversalMobile Telecommunications System (UMTS). Release 7 of “3GPP technicalspecifications” (3^(rd) Generation Partnership Project; TechnicalSpecification Group Radio Access Network) can be referred to obtaindetailed information of technical specification about the UMTS.

FIG. 1 illustrates a network architecture of UMTS. Referring to FIG. 1,the UMTS includes a user equipment (UE), UMTS terrestrial radio accessnetwork (UTRAN), and a core network (CN). The UTRAN includes one or moreradio network sub-systems (RNS), wherein each of the RNS includes aradio network controller (RNC) and one or more base stations (Node B)managed by the RNC. One or more cells exist in one Node B.

FIG. 2 illustrates a radio protocol architecture which is used in theUMTS. Radio protocol layers shown in FIG. 2 exist in the UTRAN in pairswith user equipments and are in charge of data transmission in a radiointerval. Each of the radio protocol layers will be described below.First of all, a physical (PHY) layer belonging to a first layer servesto transmit data to a radio interval by using various radio transmissiontechniques. The PHY layer is connected with a medium access control(MAC) layer, which is an upper layer of the PHY layer, through atransport channel. The transport channel is divided into a dedicatedtransport channel and a common transport channel depending on whether toshare channels.

A medium access control (MAC) layer, a radio link control (RLC) layer, apacket data convergence protocol (PDCP) layer, and a broadcast/multicastcontrol (BMC) layer exist in a second layer. The MAC layer serves to mapvarious logical channels with various transport channels and tomultiplex several logical channels with one transport channel. The MAClayer is connected with the RLC layer, which is an upper layer of theMAC layer, through a logical channel. The logical channel is dividedinto a control channel and a traffic channel depending on kinds ofinformation which is transmitted, wherein the control channel transmitsinformation of a control plane and the traffic channel transmitsinformation of a user plane.

The MAC layer is subdivided into a MAC-b sublayer, a MAC-d sublayer, aMAC-c/sh sublayer, a MAC-hs sublayer, and a MAC-e sublayer depending onkinds of a transport channel. The MAC-b sublayer manages a broadcastchannel (BCH), the MAC-c/sh sublayer manages a common transport channelsuch as a forward access channel (FACH) or a downlink shared channel(DSCH), and the MAC-d sublayer manages a dedicated channel. Thebroadcast channel (BCH) is a transport channel which is in charge ofbroadcasting of system information, the common transport channel isshared with other user equipments, and the dedicated channel is atransport channel for only a specific user equipment. Also, to supportdownlink and uplink data transmission of high speed, the MAC-hs sublayermanages a high speed downlink shared channel (HS-DSCH) which is atransport channel for downlink data transmission of high speed while theMAC-e sublayer manages an enhanced dedicated channel (E-DCH) which is atransport channel for uplink data transmission of high speed.

The RLC layer serves to assure quality of service (QoS) of each radiobearer (RB) and transmit data. The RLC layer includes one or twoindependent RLC entities for each RB to assure unique QoS of the RB, andprovides three RLC modes, i.e., a transparent mode (TM), anunacknowledged mode (UM), and an acknowledged mode (AM) to supportvarious kinds of QoS. Furthermore, the RLC layer serves to control datasize to allow its lower layer to transmit data to a radio interval. Tothis end, the RLC layer serves to generate a protocol data unit (PDU) bysegmenting and connecting service data unit (SDU) data received from itsupper layer and to forward the generated protocol data unit to its lowerlayer.

The PDCP layer is located above the RLC layer, and allows datatransmitted using IP packet such as IPv4 or IPv6 to be efficientlytransmitted in a radio interval having a relatively small bandwidth. Tothis end, the PDCP layer performs a header compression function, whichallows information necessarily required for a header part of data to betransmitted, thereby increasing transmission efficiency of the radiointerval. The PDCP layer exists only in a packet service (PS) domain dueto its basic function, i.e., a header compression function, and has onePDCP entity per RB to provide effective header compression function foreach packet service (PS).

In addition, the second layer includes a broadcast/multicast control(BMC) layer which exists above the RLC layer, wherein the BMC layerserves to perform scheduling of a cell broadcast message and broadcastfor user equipments located in a specific cell.

A radio resource control (RRC) layer located at the lowest part of athird layer is defined only in a control plane, and is related toestablishment, re-establishment, and release of RBs to controlparameters of the first and second layers. Also, the RRC layer serves tocontrol logical channels, transport channels and physical channels. Atthis time, the RB means a logical path provided by the first and secondlayers of the radio protocol for data transmission between the userequipment and the UTRAN. In general, establishment of the RB means thatcharacteristics of channels and radio protocol layers required toprovide a specific service are defined, and respective detailedparameters and operation method are established.

FIG. 3 is a flow chart illustrating a procedure according to oneembodiment of the present invention. In the embodiment of FIG. 3, anetwork transmits downlink data to a user equipment through a forwardaccess channel (FACH) which is a downlink common transport channel. FIG.4 is a diagram illustrating a protocol architecture in case wheredownlink data are transmitted to the user equipment through the FACH inaccordance with the embodiment of FIG. 3. Scheduling for downlink datatransmission through the FACH is performed in the MAC layer of Node B.It will be apparent that the features of the present invention can beapplied to downlink data transmission through another downlink commontransport channel such as a high speed downlink shared channel (HS-DSCH)in addition to the FACH.

Referring to FIG. 3, the user equipment transmits a random accesschannel (RACH) preamble to Node B through a random access channel (RACH)to initiate a random access procedure. The RACH is used to upwardlytransmit data of a short length, and some RRC messages such as RRCconnection request message, cell update message, and URA update messageare transmitted through the RACH. Logical channels such as commoncontrol channel (CCCH), a dedicated control channel (DCCH), and adedicated traffic channel (DTCH) can be mapped to the transport channel,i.e., RACH. The transport channel, RACH is again mapped to a physicalchannel, i.e., physical random access channel (PRACH).

If the MAC layer of the user equipment commands the physical (PHY) layerto perform PRACH transmission, the physical layer of the user equipmentselects one access slot and one signature and transmits PRACH preambleto the Node B [S31]. The preamble is transmitted for an access slotinterval of 1.33 ms, and one of 16 signatures is selected andtransmitted for a first certain length of the access slot. If the userequipment transmits a preamble, the Node B transmits a preamble responsemessage through an acquisition indicator channel (AICH) which is adownlink physical channel. In other words, the Node B transmits thesignature selected by the preamble for the first certain length of theaccess slot corresponding to the access slot to which the preamble istransmitted, through the AICH in response to the preamble. At this time,the Node B transmits acknowledgement (ACK) or non-acknowledgement (NACK)to the user equipment through the signature transmitted through theAICH.

If the user equipment receives ACK from the Node B through the preambleresponse message, the user equipment transmits a message part of 10 msor 20 ms to the Node B by using an orthogonal variable spreading factor(OVSF) code corresponding to the transmitted signature [S33]. If theuser equipment receives NACK, the MAC layer of the user equipmentcommands the physical layer to transmit the RACH preamble again after acertain time period. Meanwhile, if the user equipment has not receivedthe AICH corresponding to the transmitted preamble, the user equipmenttransmits a new preamble at a power higher than that of the previouspreamble by one level after a given access slot.

As described above, if the user equipment receives the preamble responsemessage which includes ACK, from the Node B, the user equipmenttransmits a message of short length through RACH message part. The RACHmessage part may include several RRC messages such as RRC connectionrequest message, cell update message, and URA update message. FIG. 3illustrates an example of transmitting a cell update message through theRACH message part. A cell update procedure is used so that the userequipment which is in Cell_FACH or Cell-PCH state can notify the UTRANof its location information at a cell level. The user equipmenttransmits the cell update message to update its location information.Since the cell update message is RRC message, it is forwarded to RNCwhere the RRC layer is located in the UTRAN.

The cell update message includes a start value related to data safetyand a cell update cause. Examples of the cell update cause that the userequipment can transmit the cell update message include the case wherethat the user equipment has data to be transmitted to an uplink inURA_PCH or Cell_PCH state, the case where the user equipment needs torespond to a paging message received from the UTRAN, and the case wherea radio link failure occurs when the user equipment is in Cell_DCHstate.

In the embodiment of FIG. 3, the cell update message further includesmeasurement information. A measurement procedure means that the userequipment measures traffic volume, channel quality, its location, etc.to provide the RNC with various kinds of information required networkmanagement and resource allocation considering a wireless environment.The UTRAN broadcasts measurement related control information throughsystem information or transmits the measurement related controlinformation to the user equipment through a measurement control message,wherein the measurement related control information is required to allowthe user equipment to perform the measurement procedure and report aresult of the measurement procedure. If a standard set to report theresult of the measurement procedure to the UTRAN in accordance with themeasurement related control information is satisfied, the user equipmenttransmits measurement information to the RNC of the UTRAN periodicallyor when a specific event occurs. The measurement related controlinformation is described in detail in the technical standard of UMTS.

Preferably, the measurement information includes information required toallow the UTRAN to control transmission of downlink data through FACHwhich is a downlink common transport channel. For example, themeasurement information may include quality information of FACH,receiving strength of a signal received in the user equipment throughFACH, quality information of a common pilot channel (CPICH) which is areference channel, information related to receiving strength of a signalreceived through the CPICH, etc. Furthermore, the measurementinformation may include control information of transmission power and/ordata rate of FACH or HS-DSCH, which is determined by the user equipment.

After receiving the cell update message from the user equipment andupdating location information of the user equipment, the RNC transmits acell update confirmation Message to the user equipment through the NodeB [S34, S35]. The RNC forwards the cell update confirmation message tothe Node B through Iub interface and also forwards power controlinformation for controlling a transmission power of the FACH or datarate control information of data transmitted through the FACH to theNode B. The power control information or the data rate controlinformation could be either a value determined by the user equipment andtransmitted to the RNC, or a value determined by the RNC from themeasurement information transmitted from the user equipment. The Node Btransmits the cell update confirmation message to the user equipmentthrough the FACH at a data rate or transmission power controlled inaccordance with the power control information. Since the FACH is mappedto a secondary common control physical channel (S-CCPCH) which is aphysical channel, controlling the transmission power or data rate of theFACH means controlling the transmission power or data rate of theS-CCPCH.

If downlink data are transmitted to the user equipment through the FACH,the S-CCPCH mapped to the FACH is transmitted using a plurality of OVSFcodes. At this time, TFCI codeword of a TFCI field of the S-CCPCH cannotify the user equipment of the number of OVSF codes along with atransport format. The relation among the TFCI codeword, a specifictransport format, and a specific number of OVSF codes can be transmittedto the user equipment through RRC message such as radio bearer setupmessage or system information. The user equipment determines S-CCPCH tobe received thereto through the RACH message or its identifier. If theuser equipment can receive the S-CCPCH transmitted by a plurality ofOVSF codes, the user equipment can identify a transport format and OVSFcodes indicated by specific TFCI codeword, through the RRC message. Theuser equipment acquires the TFCI codeword of the TFCI field of theS-CCPCH, and decodes data of the S-CCPCH, which is transmitted to thesame frame as that of the acquired codeword, in accordance with theacquired codeword.

If the user equipment cannot receive the S-CCPCH transmitted by aplurality of OVSF codes, the user equipment determines TFCI codeword,which indicate the number of OVSF codes, as an ineffective codeword, anddoes not decode data of the S-CCPCH transmitted to the same frame asthat of the TFCI codeword.

For example, as for number 1 to number 20 of the TFCI codeword, atransport format is only reported, and as for number 21 to number 40 ofthe TFCI codeword, the number of OVSF codes is reported along with atransport format. At this time, the user equipment which cannot receivethe S-CCPCH transmitted by a plurality of OVSF codes determines the TFCIcodeword corresponding to number 1 to number 20 as effective codewordand determines the other TFCI codeword as ineffective codeword.Meanwhile, the user equipment which can receive the S-CCPCH transmittedby a plurality of OVSF codes determines all the TFCI codewordcorresponding to number 1 to number 40 as effective codeword and decodesdata in accordance with the TFCI codeword.

FIG. 5 is a flow chart illustrating a procedure according to anotherembodiment of the present invention. The embodiment of FIG. 5 relates toan example of transmitting downlink data from the network to the userequipment through the HS-DSCH which is a downlink common transportchannel.

In FIG. 5, the procedure from step S51 to step S53 can refer to thatdescribed in the embodiment of FIG. 3. The RNC forwards at least a partof measurement information received from the user equipment (UE) orHS-DSCH control information acquired from the measurement information tothe Node B [S54]. The measurement information or HS-DSCH controlinformation can be forwarded to the Node B by being included in a headerpart of a data block forwarded from the RNC to the Node B. The Node Bdetermines a transmission power or data rate of HS-PDSCH which is aphysical channel, by using the measurement information or HS-DSCHcontrol information received from the RNC. The Node B transmits downlinkdata to the user equipment through the HS-PDSCH in accordance with thedetermined transmission power or data rate [S55].

According to the present invention, it is advantageous in that datatransmission through the downlink common transport channel in thewireless communication system can be adapted to change of the channelstatus.

The aforementioned embodiments are achieved by combination of structuralelements and features of the present invention in a predetermined type.Each of the structural elements or features should be consideredselectively unless specified separately. Each of the structural elementsor features may be carried out without being combined with otherstructural elements or features. Also, some structural elements and/orfeatures may be combined with one another to constitute the embodimentsof the present invention. The order of operations described in theembodiments of the present invention may be changed. Some structuralelements or features of one embodiment may be included in anotherembodiment, or may be replaced with corresponding structural elements orfeatures of another embodiment. Moreover, it will be apparent that someclaims referring to specific claims may be combined with another claimsreferring to the other claims other than the specific claims toconstitute the embodiment or add new claims by means of amendment afterthe application is filed.

The embodiments of the present invention have been described based ondata transmission and reception between the user equipment and thenetwork. A specific operation which has been described herein as beingperformed by the network may be performed by the base station or anupper node of the base station as the case may be. In other words, itwill be apparent that various operations performed for communicationwith the user equipment in the network which includes a plurality ofnetwork nodes along with the base station may be performed by the basestation or network nodes other than the base station. The base stationmay be replaced with terms such as a fixed station, Node B, eNode B(eNB), and access point. Also, the user equipment may be replaced withterms such as mobile station and mobile subscriber station.

The embodiments according to the present invention may be implemented byvarious means, for example, hardware, firmware, software, or theircombination. If the embodiment according to the present invention isimplemented by hardware, the method of transmitting downlink data in thewireless communication system according to the embodiment of the presentinvention may be implemented by one or more application specificintegrated circuits (ASICs), digital signal processors (DSPs), digitalsignal processing devices (DSPDs), programmable logic devices (PLDs),field programmable gate arrays (FPGAs), processors, controllers,microcontrollers, microprocessors, etc.

If the embodiment according to the present invention is implemented byfirmware or software, the method of transmitting downlink data in thewireless communication system according to the embodiment of the presentinvention may be implemented by a type of a module, a procedure, or afunction, which performs functions or operations described as above. Asoftware code may be stored in a memory unit and then may be driven by aprocessor. The memory unit may be located inside or outside theprocessor to transmit and receive data to and from the processor throughvarious means which are well known.

It will be apparent to those skilled in the art that the presentinvention can be embodied in other specific forms without departing fromthe spirit and essential characteristics of the invention. Thus, theabove embodiments are to be considered in all respects as illustrativeand not restrictive. The scope of the invention should be determined byreasonable interpretation of the appended claims and all change whichcomes within the equivalent scope of the invention are included in thescope of the invention.

Industrial Applicability

The present invention is applicable to a wireless communication systemsuch as a mobile communication system, a wireless Internet system, andthe like.

The invention claimed is:
 1. A method of controlling transmission ofdownlink data through a downlink common transport channel at a basestation in a wireless communication system, the method comprising:receiving, by the base station, a random access preamble from a userequipment; transmitting a response to the random access preamble fromthe base station to the user equipment; receiving, by a radio networkcontroller (RNC), a radio resource control (RRC) message on the randomaccess channel from the user equipment, the RRC message comprisingmeasurement information which includes a result of measurement performedby the user equipment; transmitting the measurement information whichincludes the result of measurement from the RNC to the base stationafter receiving the RRC message from the user equipment; anddetermining, by the base station, at least one of a data rate andtransmission power for transmission of downlink data to the userequipment on the downlink common transport channel based on themeasurement information received from the RNC.
 2. The method of claim 1further comprising transmitting the downlink data to the user equipmentaccording to the determined data rate or transmission power on aphysical channel to which the downlink common transport channel ismapped.
 3. The method of claim 2, wherein the downlink common transportchannel is a high speed downlink shared channel (HS-DSCH).
 4. The methodof claim 3, wherein the physical channel is a high speed physicaldownlink shared channel (HS-PDSCH).
 5. The method of claim 1, whereinthe upper layer message is a cell update message.
 6. The method of claim5, wherein the downlink data is a cell update confirmation message. 7.The method of claim 1, wherein the measurement information is includedin a header part of a data block to be transmitted from the RNC to thebase station.
 8. A method of receiving data through a downlink commontransport channel at a user equipment in a wireless communicationsystem, the method comprising: transmitting a random access preamblefrom the user equipment to a base station; receiving, by the userequipment, a response to the random access preamble from the basestation; transmitting a radio resource control (RRC) message comprisingmeasurement information on a random access channel from the userequipment to a radio network controller (RNC), wherein the measurementinformation includes a result of measurement performed by the userequipment; and receiving, by the user equipment, downlink data from thebase station through a physical channel mapped to the downlink commontransport channel, the downlink data transmitted from the base stationat a data rate or transmission power determined by the base stationbased on the measurement information which has been transmitted from theRNC to the base station.
 9. The method of claim 8, wherein the userequipment is in a Cell_FACH or Cell_PCH state.
 10. The method of claim8, wherein the downlink common transport channel is a high speeddownlink shared channel (HS-DSCH).
 11. The method of claim 10, whereinthe physical channel is a high speed physical downlink share channel(HS-PDSCH).
 12. The method of claim 8, wherein the downlink data is acell update confirmation message.